1. Field of the Invention
The invention relates to water treatment system control valves and, more particularly, relates to a water treatment system control valve assembly including a selector valve assembly that selectively places one of two tanks online while placing the other tank offline. The invention additionally relates to a water treatment system employing such a valve assembly and to a method of operating such a system.
2. Discussion of the Related Art
Water treatment systems (often called “water softeners”) are widely used for removing calcium and other deposit causing materials from so-called “hard water.” The typical water softener relies on an ion exchange process taking place in an ion-exchange resin bed stored in a resin tank of the water softener. As the water to be processed passes through the resin-filled tank, ions of calcium and other minerals in the water are exchanged with ions found in the resin, e.g., sodium, thereby removing objectionable ions from the water and exchanging them for less objectionable ions from the resin.
The capacity of the resin to exchange ions is finite and is reduced during the ion exchange process. If measures are not taken to regenerate the resin by replacing the undesirable ions with desirable ions, the ion exchange capacity of the resin will become exhausted. Water softeners typically are configured to periodically regenerate the ion exchange resin stored in the resin tank. Regeneration typically involves chemically replacing the objectionable ions such as calcium ions from the resin with less objectionable ions such as sodium ions. This replacement is typically performed by introducing a regenerant solution of sodium chloride or potassium chloride into the resin bed from a brine tank and thereafter flushing the regenerant solution from the bed. Regeneration of a water softener resin bed is sometimes accomplished in a direction that is co-current with the flow of water to be treated (often referred to as “downflow regeneration”) and is sometimes accomplished in a direction that is countercurrent to the flow of water being treated (often referred to as “upflow regeneration”). The resin bed is typically backwashed with treated or untreated water in order to remove trapped particulate matter, and the resin tank can be rinsed with treated or untreated water to remove objectionable soluble materials. In order to prevent interruption of service, most water softeners are configured to allow bypass flow of untreated water directly to the service lines during backwash, rinse, and regeneration. All of these operations are known in the art.
The regeneration cycle typically is controlled by a control valve or “regeneration valve” mounted on top of the resin tank. The regeneration is coupled to a source of untreated water, a treated water or service outlet line, the brine tank, a drain connection, and the resin tank. The typical regeneration valve is actuated by an electric motor under the control of a timer and/or a usage indicator to cycle the water softener from service, brine introduction, backwash, fast rinse, and back to service.
Several different types of regeneration valves have been used in water treatment systems. Some are of the rotary disc type, in which the motor rotates a three-dimensional valve element to selectively connect and cover various inlet and outlet ports in the valve body bore in which the disc is mounted. A regeneration valve of this type is manufactured by Eco Water of Woodbury, Minn. Another control valve type, manufactured by Osmonics, comprises modified poppet valves. These multiple valve elements are independently actuated by cams. Still others are of the so-called reciprocating piston type, in which the motor drives a piston to reciprocate axially in a bore to selectively connect and cover various inlet and outlet ports in the bore. One such valve is disclosed in U.S. Pat. No. 6,402,944, the subject matter of which is incorporated herein by reference.
Water treatment systems traditionally employed a single resin tank. These systems suffered the disadvantage of supplying untreated water during the system's regeneration cycle. In order to avoid this drawback, so-called “twin tank” water treatment systems have been proposed that include two tanks, each of which includes a resin bed. While one tank is online supplying treated water, the other tank is offline and is either undergoing a regeneration cycle or in a stand-by mode.
Twin tank type water treatment systems typically employ a selector valve assembly to select which of the two tanks is online and which is offline. The selector valve assemblies on the market today are of complex construction, are slow acting, and/or are relatively complex and expensive to manufacture, install, and maintain. One such valve assembly is available from Pentair, Inc. and is generally described in U.S. Pat. No. 5,628,899. The Pentair selector valve assembly includes a multi-ported, relatively slow-acting rotor that must rotate 180° over a period of time that typically is on the order of several minutes. During this switchover period, treated water may be unavailable or may be mixed with untreated water due to the short circuit of fluid flow between the various ports of the valve. In addition, and as is the case with all other commercially available selector valve assemblies, the Pentair selector valve assembly is of a complex construction that is relatively expensive to manufacture and difficult to install and maintain.
The need therefore has arisen to provide a selector valve assembly for a twin tank type water treatment system that is simpler and less expensive to manufacture, install, and maintain than prior twin tank selector control valve assemblies.
There is also a need to provide a selector valve assembly for a twin tank type water treatment system that is faster-acting than prior art valves assemblies.